No recent survey has extensively probed the Galaxy for SySt toward
directions other than low on the Plane or toward the Bulge. This is a gap
we intend to fill with the help of the GALAH survey, that is exploring the
Galaxy primarily at high latitudes. In this way a more complete census of
SySt will be possible toward all stellar populations, allowing a more
informed comparison with the predictions about the total number of SySt
spread throughout the Galaxy. Such estimates vary over a wide range: from
1,200\(-\) 15,000 of [1]}, or 3,000\(-\) 30,000 of
[2]} and [3]}, to 3,000 of
[4]}, 30,000 of [5]}, and
300,000 of [6]}. The large spread is in part
accounted for by differences in the adopted binary evolution codes and
stellar population synthesis, or by the type of SySt considered (burning or
accreting only), and also by the ratio between SySt currently in an active
state (and therefore detectable to observations) and those dormant (and
indistinguishable from single, field cool giants). The populations of SySt
containing a NS is generally estimated at 100\(-\) 1,000 (eg.
[7]}), or about 1% of those harboring a WD.
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